1. Technical Field
The present invention relates, in general, to a method of producing parvovirus antigens, and in particular, to a method of producing empty, and thus non-infectious, parvovirus capsids, and to diagnostic assays and vaccines utilizing same. The invention also relates to a method of packaging and delivering genetic information using the empty parvovirus capsids. The invention further relates to a method of packing and delivering nonparvovirus proteins, such as other antigens, ligands and enzymes, using empty parvovirus capsids.
2. Background Information
Parvoviruses are common agents of animal disease. The first strong link between parvovirus infection and human disease came from the serendipitous discovery in 1975 of parvovirus-like particles in the sera of normal human blood donors (one of the samples having been designated B19). Since that time, B19 parvovirus has been identified as the causative agent of: i) transient aplastic crisis (TAC) of hemolytic disease, ii) the common childhood exanthem called fifth disease; iii) a polyarthralgia syndrome in normal adults that may be chronic and resembles in its clinical features, rheumatoid arthritis; iv) some cases of chronic anemia and/or neutropenia; and v) some cases of hydrops fetalis. The entire spectrum of human illness caused by parvoviruses, however, is not yet clear due, in large part, to the fact that an appropriate assay is not widely available.
Parvoviruses require replicating cells for propagation, and parvovirus infection, therefore, results in pathologic changes in mitotically active host tissue. In infected children and adults, B19 parvovirus replicates in the bone marrow; in the fetus, B19 parvovirus replicates in the liver, there a hematopoietic organ. Erythroid progenitor cells are the only cell type known to be subject to infection by this virus.
The limited host and tissue range of B19 parvovirus has hampered the development of assays specific for the virus. Since the discovery of the virus, the quantity of B19 antigen available as a reagent has been limited to that obtainable from sera fortuitously obtained from infected patients. The virus has an extraordinary tropism for human erythroid progenitor cells and has only been propagated in human bone marrow cell cultures (Ozawa et al. Science 233:883 (1986)), fetal liver (Yaegashi et al. J. Virol. 63:2422 (1989)) and, to a much lesser degree, in erythroleukemia cells (Takahashi et al. J. Inf. Dis. 160:548 (1989)). The bone marrow cultures, however, require explanted bone marrow cells and, therefore, are not practical for virus propagation. The development of and availability of clinical assays continue to be limited by the availability of the antigen. The production of stable transformants capable of producing B19 protein products has been prevented by the fact that some of these products are lethal to transfected cells.